JPS603620A - Formation of fine pattern - Google Patents

Abstract

PURPOSE:To enable easy and accurate mask alignment and to form a fine pattern by forming an intermediate layer having specified light reflectance on an under substrate and a photoresist layer on the intermediate layer. CONSTITUTION:An intermediate layer 3 showing low reflectance to light (b) of wavelengths in the photosensitive range of a photoresist and high reflectance to light (a) for mask alignment is formed on an under substrate 1 having high reflectance and difference in level, and a photoresist layer 2 is formed on the layer 3 by coating. After prebaking the layer 2, mask alignment and exposure are carried out. Thus, accurate mask alignment is enabled, and a fine pattern can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an improvement in a method for forming fine patterns in the manufacturing process of semiconductor devices.

[Prior art]

In semiconductor integrated circuit devices, demands for higher density integration are becoming increasingly strict, and patterns are becoming increasingly finer. In particular, various difficulties arise when forming a fine pattern with high alignment accuracy on a base substrate with a high reflectance and a stepped portion. One example of such technology is photolithography, which involves mask alignment and exposure after forming a photoresist film. The conventional method and its problems will be explained below with reference to FIGS. 1 and 2.

As shown in Figure 1, a photoresist layer (2) is coated and formed on a high reflectivity base substrate (for example, an aluminum plate) (1) with stepped portions, and after prebaking, the above-mentioned mask alignment and When performing exposure, the reflectance of the base substrate 111 is high, so not only does the imaging contrast of the exposure pattern deteriorate, but also the light a irradiated onto the stepped portion is reflected and scattered, resulting in diffraction effects, etc. Therefore, it was difficult to obtain a highly accurate resist pattern after development.

If the absorption coefficient of the photoresist layer (2) is increased in order to reduce the influence of reflection from the underlying substrate +11, as shown in Figure 2, the light a during mask alignment will also be attenuated, causing the underlying pattern to deteriorate. Visual alignment when aligning the mask against.

Regardless of automatic alignment, there is a drawback that the signal-to-noise ratio of the alignment mark becomes small and the alignment accuracy decreases.

[Summary of the invention]

This invention was made in view of the above points, and even if there is a base substrate with a high reflectance that has a stepped portion, it has a low reflectance for light of the wavelength of the photosensitive area of the photoresist. By forming an intermediate layer that exhibits high reflectance for mask alignment light and forming a photoresist layer on top of it, mask alignment is easy.
The present invention provides a method for forming fine patterns with high precision.

[Embodiments of the invention]

FIG. 3 is a cross-sectional view showing the situation of an embodiment of the present invention, in which a substrate with a high reflectance having a stepped portion is placed on a base substrate 1ilO, which has a low light weight for the wavelength of the photosensitive area of the photoresist (for example, 436 nm). Indicates the reflectance and the light a for mask alignment
After forming an intermediate layer (3) exhibiting a high reflectance at a wavelength of 635 nm, for example, a photoresist N (2) is applied and prebaked, followed by mask alignment and exposure. This enables high-precision alignment and fine pattern formation. : A spiritual silicon (st3n4) film or a silicon oxide (S10□) film can be used as the intermediate layer (3).

The E113N4 film can be easily formed by plasma chemical vapor phase reaction, etc., and can be etched by Freon (CF4) plasma. If the underlying substrate fl+ is aluminum, it can be used as a good etching mask during chlorine-based plasma etching. There are many advantages such as: Also,
A SiO□ film can also be easily formed by applying a silanol or organosilanol solution and heat-treating it. In any case, the refractive index or film thickness may be selected so that it exhibits a low reflectance for light of the wavelength of the resist photosensitive area and exhibits an image reflectance for light for mask alignment.

In addition to determining the reflectance by selecting the film thickness and refractive index, it is also possible to determine the absorption rate of the intermediate layer for light with a wavelength in the photosensitive region of the photoresist, and for the light for mask alignment. For example, if such conditions are not met, the purpose can be achieved by mixing a dye into the intermediate layer.

〔Effect of the invention〕

As explained above, in the present invention, when forming a niphotoresist film on a base substrate, light in the wavelength range of the photosensitive area of the photoresist is poorly reflected, while light in the wavelength range for mask alignment is well reflected. Since the intermediate layer is formed and then the photoresist film is formed on it, mask alignment can be performed with high precision even with a high reflectivity base substrate with stepped portions, and fine patterning can be achieved. It is possible to form a pattern well.

[Brief explanation of the drawing]

1 and 2 are cross-sectional views for explaining the drawbacks of the conventional method, and FIG. 3 is a cross-sectional view showing the situation of one embodiment of the present invention. In the figure, (l) is the base substrate, (2) is the photoresist layer, (3) is the intermediate layer, a is the mask alignment light, and b
is the light for photoresist exposure. In addition, the same reference numerals in the figures indicate the same or equivalent parts.

Claims (4)

[Claims] (1) To form a fine pattern on the surface of the base substrate,
After forming a photoresist layer on the base substrate and performing so-called mask alignment, a photoresist layer is formed on the base substrate to expose the desired pattern to light having a wavelength of the photosensitive area of the photoresist. A method for forming a fine pattern, comprising forming an intermediate layer having a low reflectance and a high reflectance for light in the wavelength range for mask alignment, and forming the photoresist layer thereon. (2) The method for forming a fine pattern according to claim 1, characterized in that a silicon nitride film is used as the intermediate layer. (3) A method for forming a fine pattern according to claim 1, characterized in that a silicon oxide film formed by coating a base substrate with a silanol or organosilanol solution and heat-treating the intermediate layer is used as the intermediate layer. (4) A patent claim characterized in that the intermediate layer uses a layer that has a high absorbance for light in the wavelength range of the photosensitive region of the photoresist and a small absorbance for light in the wavelength region for mask alignment. The method for forming a fine pattern according to any one of items 1 to 3.